Citrate Buffer

Citrate buffer (typically a citric acid/sodium citrate system) is used at low concentrations to stabilize and adjust product pH, and the salts themselves are generally well-tolerated in patch testing. However, because its purpose is to influence pH, it can sting or exacerbate irritation on compromised barriers (e.g., eczema, post-procedure) if the final formula is even mildly acidic, so it is not completely inert. In routine leave-on and rinse-off products at appropriate pH, it is usually very gentle but still warrants caution in highly reactive skin. Safety Notes: In commercial skincare, citrate buffer systems (typically citric acid with sodium citrate and/or potassium citrate) are often used at low levels (~0.05–0.3%) to fine-tune pH in leave-on creams/serums and cleansers without materially impacting skin feel. Higher total buffer loads are seen in consumer-available high-acid products (AHA/BHA exfoliating toners, peels, and some acne/brightening formulas) where stronger buffering is needed to control pH and stability, commonly ~0.5–2% and occasionally up to ~3% total citrate buffer in OTC products. Rinse-off products may use similar or slightly higher levels than leave-on when neutralizing surfactant systems or stabilizing low-pH formulas, but concentrations above ~3% are uncommon in mainstream OTC due to irritation risk and formula constraints.